BIOMES

Biomes: Many places on the earth share similar climatic, topographic, and soil conditions, androughly comparable communities have developed in response to analogous conditions in widelyseparated locations. These broad types of biological communities are called biomes.Temperature and precipitation are among the most important determinants in biome distribution. Ifwe know the general temperature range and precipitation level, we can predict what kind ofbiological community is likely to develop on particular site if that site is free of disturbance for asufficient time.TERRESTRIAL BIOMES

The figure above shows the relationships of average temperature, annual precipitation and thecorresponding biomes that could possibly exist.Deserts

Characterized by low moisture levels and precipitation that is both infrequent and alsounpredictable from year to year.With little moisture to absorb and store heat, daily and seasonal temperatures can fluctuatewidely.Precipitation less than 2.5 cm support almost no vegetation; 2.5- cm: sparse vegetation (less1

than 10% of ground covered

Plants in this harsh climate need a variety of specialization to conserve water and protect tissuesand thick epidermal layers help reduce water loss.Spines or serrated leaf edges discourage predators.Animals of the desert have both structural and behavioral adaptations to meet their three mostcritical needs: food, water and heat survival.Desert animals escape the main onslaught of daytime heat by hiding burrows or rocky shelterfrom which they emerge only at night. Pocket mice and kangaroo rats get most of the moisturethey eat from the grains they eat.They have many adaptations to conserve water such as producing highly concentrated urine andnearly dry feces that allow them to eliminate body wastes without losing precious moisture.

Grasslands: Prairies and Plains

Grasslands are rich biological communities of grasses, seasonal herbaceous flowering plants andopen savannas.Seasonal cycles for temperatures and precipitation contribute to abundant vegetative growththat both protects and enriches the soils of these prairies and plains, making them among therichest farmlands in the world.Grasslands have few trees because of inadequate rainfall, large daily and seasonal temperatureranges, and frequent grass fires that kill woody seedlings.In many parts of the world, native people have used fire to maintain grasslands and improvehunting.Fire suppression and conversion of the rich prairie soil to farmland have greatly reduced nativegrasslands everywhere. Some prairie lands grow wheat, corn, oats, sunflowers and othercultivated crops.Lands that are less suited for crops because of limited water availability are used mainly asrangeland.Animals include wolves, deer, elk and pronghom antelopes.Hunting, wetland drainage, introduction of alien species and other human modifications to theland have greatly diminished most wildlife populations.

Tundra

Climates in high mountain areas or at far northern or southern latitudes are often too harsh fortrees. The treeless landscape called tundra is characterized by a very short growing season; cold,harsh winters, and the potential for frost any month of the year.Although water may be abundant on the tundra, for much of the year it is locked up in ice orsnow and therefore unavailable to plants.As far as plants are concerned, the tundra is a very cold desert.Arctic tundra is biome of low productivity, low diversity and low resilience. Winters are long anddark. Only the top several centimeters of the soil thaw out in the summer, and the lower soil ispermanently frozen permafrost. This frozen layer prevents snowmelt water from beingabsorbed into the soil, so the surface of soil is waterlogged during the summer.Alpine tundra differs from the arctic tundra. Thin mountain air permits intense solarbombardment, especially by ultraviolet radiation, thus many alpine plans have deeppigmentation that shields their inner cells. Alpine soil is windswept and often gravelly or rocky.The sloping terrain cause moisture to drain quickly.Tundra may swarm with life during the brief summer growing season. However, few species areable to survive the harsh winters or migrate to warmer climates.Dominant plants are dwarf shrubs, grasses, mosses, lichens. Animals include muck ox, caribou,or alpine mountain goats and mountain sheep.Many animals hibernate during winter. Flocks of migratory birds nest on the abundant summerarctic wetlands.Damage to tundra is slow to heal. At present, the greatest threat to this distinctive biome is oiland natural gas wells in the Arctic and mineral excavation in mountain regions.Some of the most promising sites for oil exploration or mining are summer feeding and breedinggrounds for animals such as caribou, grizzly bears, or mountain sheep.

Temperate Needle-leaf Forests

Conifer (cone-bearing trees) dominates certain distinctive biomes.

Moisture is limited by sandy soil, low precipitation, or short growing season. The plants reducewater loss by evolving thin, needle like evergreen leaves with a thick black waxy coating.Soft leaves of deciduous trees, conifer needles and scales can survive harsh winters or extendeddroughts and can accomplish some photosynthesis under poor conditions.Common deciduous trees: birches, aspens, and maples.Mountain regions around the world support coniferous forest where water availability is limitedby climate or topography.At very high elevations, just below the alpine tundra, we find a picturesque stunted forestcharacterized by twisted, wind-sheared willows,, white bark pines and alpine firs.The coniferous forests of the pacific coast represent a special set of environmentalcircumstances. California redwood, the largest trees in the world and largest organisms of anykind to have existed.

Broad-leaved Deciduous and Evergreen forests

Forests of broad-leavened trees occur throughout the world where rainfall is plentiful.A key adaptation of deciduous trees is the ability to produce summer leaves and then shed themat the end of the growing season.Examples: oak, maple, birch, beech elm, ash and other hardwoods. These tall trees form a forestcanopy over a diverse understory of smaller trees, shrubs, and herbaceous plants, includingmany annual spring flowers that grow, flower, set seed and store carbohydrates before they areshaded by the canopy.

Where climate is warm year-round forests are dominated by evergreen trees such as the liveoaks and cypresses.

Tropical Moist Forests

The human tropical regions of south and central America, Africa, Southeast Asia and some of thePacific Islands support one the most complex and biologically rich biome types in the world.Although there are several kinds of moist tropical forests, they share common attributes ofample rainfall and uniform temperatures.Cool cloud forests are found high in the mountains where fog and mist keep vegetation wet allthe time.Tropical rainforests occur where rainfall is abundant-more than 200 cm per year andtemperatures are warm to hot year-round.The soil of both these tropical moist forest types tends to be old, thin, acidic, and nutrient-poor,yet the number of species present can be mind-boggling. For instance, the Malay Peninsula hasabout 8,000 species of flowering plants. Great Britain, which has twice the land area but only1,400 species.The number of insect species found in the canopy of tropic rainforests has been estimated to bein the millions.It is estimated that one-half to two-thirds of all species of terrestrial plants and insects live in thetropical forests. This diversity is the result of the great variety of habitats and nicheopportunities available and the long history of these ecosystems.The nutrient cycles of these forests are unique. 90% of the nutrients in the system are containedin the bodies of the living organisms. The growth in tropical rainforests depends on the rapiddecomposition and recycling of dead organic materials. Leaves and branches that fall to theforest floor decay and are incorporated almost immediately back into living biomass.When the forest is removed for logging, agriculture, and mineral extraction, the thin soil cannotsupport continued cropping and cannot resist erosion from the abundant rains.

If the cleared area is too extensive, the rainforest community cannot repopulate it.Rapid deforestation is occurring in many tropical areas as people move into the forests toestablish farms and ranges but the land soon loses its fertility.In 1970s the chemical defoliation in Vietnam with Agent Orange systematically destroyed largeareas of Southeast Asian rainforests, as well as the coastal mangrove swamps.

Tropical Seasonal Forests.

Many areas in India, Southeast Asia, Australia, West Africa, and West Indies and South Americahave tropical regions characterized by distinct wet and dry seasons instead of uniform heavyrainfall throughout the year. Temperatures are hot year-round. These areas have produced communities of tropical seasonalforests: semi evergreen or partly deciduous forests tending toward open woodlands and grassysavannas dotted with scattered, drought-resistant tree species. Tropical dry forests have typically been more attractive than wet forests for human habitationand have suffered greater degradation. Clearing a dry forest with fire is relatively easy during the dry season. Soils of dry forests havehigher nutrient levels and are more agriculturally productive than those of a rainforest. They have fewer insects, parasites, and fungal diseases than a wet forest makes. Dry or seasonalforests are healthier place to live.

AQUATIC ECOSYSTEMSFreshwater and Brackish Ecosystems

Freshwater ecosystems - include the standing waters of ponds and lakes as well as the flowingwaters of rivers and streams. There are also some unique freshwater ecosystems, includingunderground rivers and subterranean caves.Freshwater ecosystems are influenced by characteristics of local climate, soil, residentcommunities and surrounding terrestrial ecosystems.The biological communities of freshwater ecosystems are limited and largely determined by thephysical characteristics of the environment.The basic needs of terrestrial organisms: carbon dioxide, water and sunlight for photosynthesis,oxygen for respiration; and food and mineral nutrients for energy growth, and maintenance.Site characteristics that influence the availability of these necessities include:1. Substances that are dissolved in water, such as oxygen, nitrates, phosphates, potassiumcompounds and other by-products of agriculture and industry.2. Suspended matter, such as silt and microscopic algae, that affect water clarity and thereforelight penetration.3. Depth4. Temperature5. Rate of flow6. Bottom characteristics (muddy, sandy, rocky)7. Internal convective currents8. Convection to or isolation from other aquatic ecosystems.

The biological communit ies of freshwater ecosystems are limit ed and largelydetermined by the physical characteristics of the environment.9

Vertical Stratification - is an important aspect of standing water ecosystems, especially in regards to

gradients of light temperature, nutrients and oxygen. Organisms tend to form distinctive verticalsub-communities in response to this stratification of physical factors.1. The plankton community consists of microscopic plants, animals and protists that float freelywithin the water column2. Non-planktonic organisms are specialized to live at the air-water interface (e.g. insects suchas water striders) and other are able to swim freely in the open waters (e.g. fish)3. Bottom dwellers (e.g. snails, burrowing worms and insect larvae, bacteria) make up thebenthos or bottom communities.Layers of Deep Lake:Open Water

Not all freshwater lakes contain what we would consider "fresh" water. The Caspian Sea, DeadSea, Great Salt Lake and numerous other salty lakes have been formed by evaporative shrinkageof large bodies of water.Deserts may have alkaline or arsenic-containing lakes and potholesStill other salty and mineral-rich ponds and lakes are fed by mineral hot springs.

10

Estuaries and Wetlands, Transitional Communities

Estuaries are bays or semienclosed bodies of brackish water that form where rivers enter the ocean. Estuaries usually contain rich sediments carried downriver, forming shoals and mudflats thatnurture a multitude of aquatic life. Estuaries are sheltered from the most drastic ocean action but do experience tidal ebbs andflow. Daily tides may even cause river levels to rise and fall far inland from the river mouth. > They aresignificant "nurseries" for economically important fish, crustaceans (such as crabs and shrimpsand mollusks (such as clams, cockles and oysters) Where the continental shelf is broad and shallow, an extensive fan-shaped sediment depositcalled delta may form at the river mouth. Deltas often are channeled by branches of the rivers,creating extensive coastal wetlands that are apart of the larger estuarine zone.

Wetlands are ecosystems in which the land surface is saturated or covered with standing water atleast part of the year and vegetation is adapted for growth under saturated conditions.

On sources of water- Swamp and marshes tend to be associated with flowing water.- Fens are fed by groundwater and surface runoff

11

Bogs are fed by precipitation

On productivity:- Swamps and marshes have high productivity- Bogs and fens have low productivity.

On physical conditions:- Swamps and marshes have shallow water to allow full penetration of sunlight and seasonalwarming. These mild conditions favor great photosynthetic activity resulting in highproductivity at all trophic levels.- Wetlands are major breeding, nesting and migration staging areas for waterfowl and shorebirds.

Significant ecosystem services of Wetlands:

-

They support a great diversity of life forms.

Their role in planetary water relationships: Wetlands act as traps and filters for water that moves through them. Runoff water is slowed as it passes through shallow, plant-filled areas, reducing flooding. As a result, sediments are deposited in the wetlands instead of travelling into rivers andeventually oceans, m this way, wetlands both clarify surface waters and aid in theaccumulation and formation of fertile land.Chemical interactions in wetland ecosystems neutralize and detoxify substances in thewater.Water in wetlands seeps into the ground, helping to replenish underground water reservoirscalled aquifers.Wetlands convert naturally to terrestrial communities largely through sedimentation,Eutrophication or stream cutting and draining.Destruction of wetlands is of great concern because it means loss of ecological services tothe biosphere, as well as loss of essential habitats for myriad of species.

12

Shorelines and Barrier Islands

Ocean shorelines, including rocky coasts, sandy beaches and offshore barrier islands are particularlyrich in life forms. Rocky shorelines support and incredible density and diversity of organisms that grow attachedto any solid substrate. Sandy shorelines provide homes for organisms that live among the sand grains and in burrows. Grasses and trees that hold the dunes are destroyed, destabilizing the soil system and increasesusceptibility to wind and wave erosions Insurance is expensive because of the hazards of natural erosion and storms Building and maintaining sea walls are expensive and a continuous process

Barrier islands protect inland shores from onslaught of the surf, especially during severe storms. They are not permanent. The sands are constantly being redistributed by wind and water.

13

Oceanic Islands and Reefs

Oceanic islands demonstrate interesting ecosystems because of the different ways they originateand the patterns by which organisms colonize them. Islands that break away or isolated from a continental landmass Volcanic and coral island communities

Coral reefs form in clear, warm, tropical seas and are particularly well-developed in the southPacific. They are the accumulated calcareous skeletons of innumerable tiny colonial animals calledcorals. Each of the interconnected coral animals builds calcium carbonate chamber on the surface ofthe accumulated secretions of previous generations of animals Coral reefs usually form along the edges of shallow, submerged banks or shelves The depth at which they form is limited by the depth of sunlight penetration. Coral reef communities rival tropical forest communities in species diversity, number ofindividuals, and brilliance of color and interest forms of both plants and animals.